The main objective of this proposal is to investigate the role of cholesterol homeostasis in the pathogenesis of age-related macular degeneration. Although several reports suggest that aberrant cholesterol metabolism may play a role in AMD pathogenesis, the underlying cell biology of this process is unclear. Published work from our laboratory demonstrates that the lipofuscin component A2E delays the degradation of rod outer segment lipids in retinal pigment epithelial (RPE) cells without affecting protein processing. The first specific aim of this proposal will extend this work by investigating the mechanistic aspects of A2E-induced phospholipid and cholesterol accumulation in the RPE. Lysosomal lipase activities, transcriptional activation and enzyme-substrate interactions will be studied in the presence and absence of A2E. The second specific aim will examine the roles of the LDL receptor, the scavenger receptor class B type l, caveolin-1 and the ATP-binding cassette transporter A1 in polarized lipoprotein internalization and cholesterol/phospholipid efflux pathways in the RPE and investigate how A2E affects these processes.